Igniter for rocket propellant



Sept. 19, 1961 w. G. STANLEY IGNITER FOR ROCKET PROPELLANT 2Sheets-Sheet 1 Filed Nov. 6, 1956 INVENTOR. William 6. Stanley m QMATTORNEY Sept. 19, 1961 w. e. STANLEY IGNITER FOR ROCKET PROPELLANT 2Sheets-Sheet 2 Filed NOV. 6, 1956 OOOOOOO OOOOOOOOOOO OOOOOOOOQOO 76INVENTOR.

William 6. Stanley BY I M 77 32 3/ /9 Fig. 3

ATTORNEY United States Patent 9 3,000,311 IGNITER FOR ROCKET PROPELLANTWilliam G. Stanley, Seymour, Ind., assignor to Standard Oil Company,Chicago, 111., a corporation of Indiana Filed Nov. 6, 1956, Ser. No.620,768 4 Claims. (Cl. 102-70) This invention relates to rocketpropulsion and gas generation. More particularly it relates to anigniter for ammonium nitrate-type propellants,

In the military usage of solid propellants for rocketry and gasgeneration it is a requirement that the propellants be operative overthe broad temperature range between about 70 F. and +130 F. Because oftheir relative cheapness ammonium nitrate based solid propellants arecoming into prominence as solid propellants in the military field.Ammonium nitrate-type solid propellants are frequently sensitive totemperature and the combustion of the propellant can be initiated at thelowest atmospheric temperatures only with difliculty. Sometimes theproblem can be overcome by modifying the composition of the propellant.However, such modifications frequently introduce problems at moreelevated temperatures.

An object of the invention is an igniter which is suitable for ignitingthe combustion of ammonium nitrate based propellants at all atmospherictemperatures. A particular object is an igniter assembly suitable forinitiating combustion of ammonium nitrate propellants which aredifiicult to ignite the combustion thereof. Other objects becomeapparent in the course of the detailed description.

The igniter assembly of the instant invention comprises an igniterassembly comprising a vessel, having an open end, an igniter mixture,positioned in said vessel, consisting essentially of (a) a powder memberselected from the class consisting of black powder, magnesiumpowderpotassium nitrate mixture, aluminum powder-potassium nitratemixture, aluminum powder-alkali metal perchlorate mixture and magnesiumpowder-alkali metal perchlorate mixture and (b) lumps consistingessentially of ammonium nitrate, an oxidizable binder and a combinationcatalyst, the ammonium nitrate being the predominant component, saidlumps having a minimum dimension of at least about inch and a maximumdimension of not more than about /8 inch, said igniter mixturecontaining an amount of said powder member at least sufiicient toinitiate sustained combustion of said lumps, readily destructible meansfor maintaining said mixture within said vessel and means, positionedwithin said vessel, adapted for initiating burning of said powdermember.

It has been found that ammonium nitrate propellants need to be broughtup to a more or less definite temperature in order to initiate sustainedcombustion of the surface of the propellant. A difficulty with the moreor less conventional black powder or powdered metal-nitrate orperchlorate mixtures is that the duration of the combus tion of theigniter is so short that the ammonium nitrate propellant is not broughtat its surface to a temperature high enough to sustain combustion; orthe volume of gases produced by the igniter is so small that asufficient area of the propellant is not caused to burn and therebysustained burning is not attained. This problem has been overcome byusing as the igniter a mixture of the conventional black powder orpowdered metal-nitrate or perchlorate mixtures with small lumps of anammonium nitrate-type propellant. Suflicient amount of the black powderor powdered metal-nitrate or perchlorate material is present in theigniter to initiate sustained combustion of the surfaces of the lumps ofammonium nitrate-type propellant. The lumps of propellant are of such asize and amount that sufiicient volume of hot gases are proice duced foralong enough time to initiate sustained combustion of the ammoniumnitrate propellant which is to be ignited either in a rocket motor or agas generator. The powder member of the igniter mixture is preferablyblack powder. The coarser grained black powder known as blasting powderis particularly suitable. A description of black powder, andparticularly blasting powder, which are suitable for use in the ignitermixture of this invention is contained in the Blasters Handbook. Whenoperating with ammonium nitrate-type propellants that are particularlydilficult to ignite it is preferred to use black powder which has anaverage screen size between about A and A; inch. These may be obtainedby the use of the C grades of blasting powder available commercially.

Instead of black powder the igniter mixture may be any one of themixtures of powdered aluminum or magnesium metal in conjunction withpotassium nitrate or alkali metal perchlorates. For example, a mixtureof about equal parts by weight of aluminum powder and potassiumperchlorate is particularly suitable as the powder member of the igniterof this invention. This mixture is available commercially as Alclo.Mixtures of powdered aluminum metal or powdered magnesium metal withpotassium nitrate powder are suitable for use as the powder member.Mixtures of powdered magnesium metal and potassium or sodium perchlorateare suitable for use as the powder member of the igniter.

In addition to the use of straight black powder as the powder member ofthe igniter of the invention there may be used mixtures of magnesiumpowder or aluminum powder and black powder. Such mixtures are well knownin the fireworks industry and are used in pyrotechnic displays.

The ammonium nitrate propellant lumps present in the igniter mixturemust be of a size such that the lumps will not be consumed completelyuntil the propellant body has obtained a sustained combustion. It is tobe understood that the propellant to be ignited could be made from thesame material as the lumps are made and these lumps are properlydesignated as ammonium nitrate-type propellant material. In thisdescription the term propellan is generally intended to mean the body ofammonium nitrate based material which drives the rocket or which burnsto produce gases in a gas generator or acts as a booster charge or isthe driving force in an assistedtake-otf unit. In this description theammonium nitratetype propellant which forms the lump portion of theigniter mixture of this invention is spoken of as lumps of propellant orthe lump member of the igniter mixture.

In general the lumps of propellant may be either uniform shapes such assmall spheres, oval pills, irregular fragments from crushing of largemasses of material or parallelepipeds of various shapes. The preferredconfiguration of the lumps is approximately cubical with a secondarypreference for parallelepiped's having rectangular surfaces. Usually thelumps are solid but under some conditions the lumps may be perforated inorder to increase the burning surface and reduce the burn out time ofthe igniter mixture.

The lumps of propellant present in the igniter mixture should have aminimum dimension of at least about inch and a maximum dimension of notmore than about A; inch. For example, cubical lumps might be A; inch ona side or may be as much as inch on a side. Another lump having a slabshape may be 4 inch in one dimension by inch on another side and /2 inchin the third dimension. Spherical lumps may have a diameter varying fromabout /8 inch to as much as /3 inch. It is to be understood that theparticular configuration of the lump will be determined by thecomposition of the propellant forming the lump and also by thecomposition of the rocket propellant to be ignited. Since militarypropellants must be readily ignited on the broad temperature range theigniter mixture will almost always be adapted to initiate sustainedcombustion of the main body of propellant at temperatures on the orderof -70 F.

The igniter mixture must contain at least enough of the powder member toinitiate sustained combustion of the lump member. The amount of powdermember will be determined by the composition of the powder member aswell as by the composition of the lump member. When utilizing as thepowder member black powder having an average screen size between A andinch, it is preferred to have as the igniter mixture between about 3parts by weight of powder member per part or lump present and about 1part by weight of powder member per part of lump present,

The lumps are formed from ammonium nitrate propellant consistingessentially of ammonium nitrate oxidizable binder and a combustioncatalyst. The lumps are formed by intimately mixing powdered ammoniumnitrate, the binder and a combustion catalyst.

The combustion catalyst present in the lump propellant may be any one ofthose known to the art for use with ammonium nitrate explosives andammonium nitrate propellants. The better known combustion catalysts areinorganic compounds of chromium, iron or copper for example, ammoniumdichromate, chromic oxide, cupric oxide, yellow ferric oxide, Prussianblue, the various heavy metal cyanides and the various heavy metalcyanamides. Organic combustion catalysts are also known, a particularlysuitable one is sodium barbiturate. Although finely divided carbon isnot generally considered a combustion catalyst for ammonium nitrate itis present in moderate amounts and vastly increases the sensitivity ofammonium nitrate containing propellants; therefore herein finely dividedcarbon is considered as a combustion catalyst particularly incombination with one of the above designated inorganic or organiccatalysts.

The binder portion of the lump member may be any oxidizable orcombustible material which will permit the formation of a suitableconfiguration of ammonium nitrate powder, combustion catalyst powder andbinder. The binder is oxidizible in order to take advantage of the freeoxygen produced in the decomposition of ammonium nitrate. The binder isgenerally a thermoplastic material containing carbon, hydrogen andusually oxygen atoms. Also the binder may be a thermosetting organicmaterial. Thus the lump member may be produced by intermingling ammoniumnitrate powder catalyst and chemical reagents which under the action ofheat react to form resinous or polymeric materials which set to form asuitable configuration having the appearance of a solid. Thesethermosetting materials may be of very high molecular weight polyesters,thiokol rubbers, vinyl pyn'llidone rubber, etc.

Thermoplastic binders are preferred because of the ease of preparationof the lump member. The thermoplastic binders may be a unitary materialsuch as a petroleum asphalt or a multi component solution. In generalthe thermoplastic binders consist of a polymer or resin to providestrength and a single or dual plasticizer to impait sufiicientthermoplastic characteristics to the binder. Examples of strengthaffording materials are cellulose acetate of various acetic acidcontents, cellulose acetate butyrates of various acid contents cellulosepropion-ates (the cellulose derivatives are available over the entirespectrum of acid contents), polyvinyl acetate, polyvinyl chloride,mixtures of these two polystyrenes, and styrene acrylonitrile. Thislisting is not inclusive of all possible materials suitable.

The plasticizers may be any one of the multitudinous numbers known tothe plastic art as suitable for plasticizing polymers and resins of thetypes set out above. Reference to any Plastics Handbook will producesufi"1 cient representatives of these materials.

In general the lump ammonium nitrate propellant will contain at leastabout 65 weight percent of the ammonium nitrate and from about 2 to 5weight percent of combustion catalyst, the remainder of the compositionwill consist of binder and possibly a few of other materials which aredesigned to improve the stability of the composition or act as ignitionpromoters for example, diphenyl amine is added to improve the stabilityat high temperature. Small amounts of surfactants are frequently used toimprove the forming of the binder.

Examples of ammonium nitrate propellant compositions which have beenfound suitable for use as the lump member of the igniter mixture of thisinvention are set out below. Ammonium nitrate 72%, ammonium dichromate2%, binder 24%; the binder consisted of 25% of lacquer grade commercialcellulose acetate, 37% of dinitrodiphenyl oxide and the remainder apolyester condensation product of ethyleneglycol and diglycolic acid.Ammonium nitrate 73%, Prussian blue 4% and the remainder binder havingthe approximate composition set out in the preceding propellant.Ammonium nitrate 74%, magnesium nitrate 2%, ammonium dichromate 2%, andthe remainder binder; the binder consisted of 31% of cellulose acetatebutyrate and 69% of 2,4-dinitrodiphenyl oxide. Ammonium nitrate 76%,ammonium dichromate 2%, Prussian blue 1%, and the remainder binder; thebinder consisted of polyvinyl chloride, 25 dinitrodiphenyl oxide anddinitrophenyl allyl ether in equal parts. Ammonium nitrate 83%, Prussianblue 3%, carbon black 2%, and the remainder binder; the binder consistedof polyvinyl chloride 25 dinitrophenyl allyl ether 25 dinitrodiphenyloxide 30%, and dinitrotoluene 20%. Ammonium nitrate 76%, Prussian blue3%, carbon black 1%, and the remainder binder; the binder consisted ofpolyvinyl acetate 25 and bis- (dinitrodiphenyl) triglycol ether 75%. Thepolyvinyl acetate composition of the preceding sentence is modified bythe presence of about 1% each of diphenyl amine and urea. Ammoniumnitrate 70%, carbon black 3%, diamino toluene 1%, sodium barbiturate 3%and the remainder binder; the binder consisted of cellulose acetatelacquer grade 28%, asphalt 8%, acetyl triethyl citrate 34%,dinitrophenoxy ethanol 30%. Ammonium nitrate 79%, Prussian blue 3%,carbon black 2% and the remainder binder; the binder consisted ofroofing asphalt 65%, polyisobutylenes 100,000 M.W. 11% anddinitrophenylethyl acetate 34%. Ammonium nitrate 79%, Prussian blue 3%and the remainder binder; the binder consisted of roofing asphalt 30%,styrene acrylo nitrile 29%, acrylonitrile units 20%, dinitrotoluene 20%and dinitrodiphenyl oxide 30%. Ammonium nitrate 77%, Prussian blue 1%,ammonium dichromate 2%, and the remainder binder; the binder consistedof styrene acrylonitrile 25%, dinitrodiphenyl oxide 31%, dinitrophenylallyl ether 31%, dinitrostilbene 4% and rosin, 200F. softening point,9%.

Example 1 In this example a gas generator suitable for use in thecartridge shown in the illustrations could not be ignited attemperatures of 40 F. and below by the use of a black powder ignitermixture consisting of 70 grams of CCC grade blasting powder havinggrains about /2 inch in sieve size.

A mixture consisting of 45 grams of this CCC blasting powder and 25grams of lumps of propellant initiated sustained combustion of thepropellant at temperatures below 70 F.

An igniter mixture consisting of 40 grams of CCC blasting powder and 15grams of lumps of propellant was able to initiate sustained combustionof a gas generator propellant at 70 F. In both instances the lumps ofpropellant utilized in the igniter mixture were cubes approximately inchon a side.

The composition of the lump propellant was ammonium nitrate 80%,Prussian blue 3%, carbon black 1%,

diaminotoluene 1%, and the remainder binder; the binder consisted of 25%dinitrophenyl propyl ether, 25% dinitrodiphenyl oxide, 20% styreneacrylonitrile and 30% roofing asphalt. The ingredients were thoroughlyintermingled at about 100 C. and cast into a slab; after the slab hadcooled it was cut into cubes about inch on a side. The proper amount ofcubes and blasting powder were then intermingled by simple shaking in asmall cup and poured in a random mixture into the igniter. (Thepropellant had this same composition except that sodium barbiturate wassubstituted for Prussian blue.)

Example 2 In this example the igniter mixture consisted of irregularlumps of ammonium nitrate propellant ranging in size from about A; toinch. The igniter mixture consisted of FFF grade black powder andaluminum powder. This igniter mixture was successful in startingammonium nitrate propellant at low temperature, which the powder memberalone was unable to do.

In this instance the lump member had the same composition as thepropellant being ignited. The composition of the propellant was ammoniumnitrate 72.6%, Prussian blue 2%, yellow ferric oxide 1% and theremainder binder; the binder consisted of lacquer grade celluloseacetate 20%, dinitrodiphenyl oxide 40%, and polyester condensationproduct of ethyleneglycol and dirglycolic acid 41% Example 3 In thisexample the igniter mixture consisted of lumps of the ammonium nitratepropellant composition of Example 2. The powder member consisted ofabout equal parts by weight of powdered magnesium and potassium nitrate.This igniter mixture not only initiated combustion of the body ofpropellant having the same composition as the lump member but alsomarkedly reduced the thrust surge caused by the brisance of themagnesium powder-potassium nitrate mixture.

The igniter assembly of the invention is described in detail and its usein a gas generator operation in connection with the annexed figures willform a part of this specification.

FIGURE 1 shows a partial section of one embodiment of an igniterassembly.

FIGURE 2 shows a plan view looking into the cup of the igniter assemblyof FIGURE 1.

FIGURE 3 shows a section of a gas generator cartridge utilizing theembodiment of FIGURE 1.

FIGURE 4 is a partial section plan view of the cartridge of FIGURE 3.

The figures show in detail a gas generator cartridge suitable for use inturbojet starting. It is to be understood that this is only one of manyplaces in which the igniter assembly of the instant invention may beused.

One of the simplest techniques now used for starting turbojet enginesinvolves an auxiliary engine, called a turbojet starter, which auxiliaryengine or starter turns over the main turbojet rotor and brings it up tothe desired rotational speed before the injection of the fuel 'into thecombustors. This turbojet starter comprises a gas-driven turbine whichis connected, through gearing, to a clutch and the entire assembly isthen mounted on the frame of and coupled to the shaft of the mainturbojet rotor. The gas for driving the starter turbine is derived fromthe combustion of a solid propellant. The solid propellant is burned ina chamber which is mounted integrally as a part of the starter. Thischamber is formed to receive a starter cartridge and is designed to beopened and closed manually. The chamber is divided at about itsmid-portion into a lower section and an upper section; the two portionsare locked together by an ordinary slip joint, which slip joint is notgas tight. This type of sealing means is used rather than a gas typescrew thread in order to permi-tmanual operation without the use oftools. The solid propellant, whose combustion produces the gases thatturn over the starter turbine, is contained in a cartridge case which isdesigned to fit into the starter chamber.

The igniter assembly is described in detail in connection with 'FIGURES1 and 2. The igniter cup 11 is a shallow metal cup relatively wide inrelationship to its depth. This relationship is in order to provide aburst of ignition gases covering a large portion of the end of startergrain and also in order to reduce the total length of the startercartridge case. The shell of the cup is turned over at the ends in orderto strengthen the cup. There is centrally located in cup 11 a holewherein the electrical conducting elements are positioned. Tubularbushing 12 is fitted in this hole. The inner end of tubular bushing 12is crimped over to form a tight fit between the metal of cup 11 and thebushing 12. An electrical conductor 14 is fastened to bushing 12 insidecup 11. In this instance, connection 14 is a copper washer and theconnection is made by crimping the inner end of bushing 12 over washer14. A female clamp electrical terminal 16 is fastened on to washer 14 inorder to provide a connection for the wires of an electrical squib. Anelectrical conducting rod 17 passes through the interior of bushing 12and extends from the inside of cup 11 to point somewhat beyond the outerend of said bushing to form an electrical contact point. In thisembodiment, the end of rod 17 has been expanded to form a broad contactpoint 18. At the inside end of rod 17 there has been attached a femaleelectrical clamp 19 to which the electrical leads of a squib areattached. The contact end 18 of conducting rod 17 is insulated from theinterior of bushing 12 by means of an elastic moisture-imperviousinsulating means 21. Means 21 may be any elastic material which is notan electrical conductor and at the same time will prevent the ingress ofmoisture into the conduit formed by bushing 12. Silicone rubber isparticularly suitable. A reinforcing and insulating washer is positionedbelow insulating means 21 in the conduit formed by bushing 12. Thisinsulating means may be a simple paper washer. Below this Washer thereis positioned about rod 17 in the conduit of bushing 12 a tubularinsulating means preferably of silicone rubber. This tubular elementinsulates rods 17 from bushing 12. The contact end 18 of rod 17 isrigidly maintained in predetermined relation with the outer end ofbushing 12 by a fastening means positioned about rod 17 inside the cup.In this embodiment, a washer 26 is forced against the crimped end ofbushing 12 by means of fastener 27. Other means for maintaining thecontact end at the predetermined position while insulating rod 17 fromthe lower end of the bushing 12 may be readily devised.

The ignition device comprising the cup and the electrical conductionmeans are rigidly attached to the hole provided in the end-closure ofthe shell of the cartridge in such a way that the contact point 18 isexposed beyond the outside wall of the end-closure. In FIGURE 1, thereis shown one means of having this fastening. In this embodiment, theoutside of the portion of bushing 12 extending outside of shell 11 isthreaded and the igniter assembly is fastened to the end-closure bymeans of nut 31. Nut 31 is also shown in FIGURE 3. It is preferable thatsome means of vibration-proofing nut 31 be provided and in FIGURE 3 lockwasher 32 is provided. The security of the igniter assembly may befurther enhanced by having the radius of the curvature of cup 11slightly greater than the radius of curvature of the end-closure. Thuswhen the ignition device is fastened by means of nut 31 the curvedportion of cup 11 is forced into conformity with the curvature ofend-closure, thereby providing an almost vibration-proof fit between theigniter assembly and the end-closure.

In FIGURE 2, electrical squibs 33 and 34 are shown in position inside ofcup 11. Cup '11, containing the squibs, is then filled with theparticular igniter mixture utilized in the specific embodiment of thestarter cartridge. It is necessary to close the end of cup 11 to keepthe ignition mixture in place and also to have a moisture-imperviousprotection for the ignition mixture. A moisture-impervious film may beplaced over the open end of cup 11 and then fastened by some fasteningmeans passing around the rim 36 of cup 11. Another form of closure forcup 11 is made of moistureimpervious elastic material provided with aflange which snaps over rim 36 of cup 11. It is necessary that themoisture-impervious fi-lm closing beyond the cup 11 be held securelyenough to avoid any slipping-off of the film during handling and alsostrong enough to avoid rupture of the film during handling. In theparticular embodiment set out herein, the end of cup 11 is closed bymeans of a moisture-resistant paper 38 positioned over the open end ofcup 11 and passing down the sides of the cup in an overlapping manner.Over the moistureresistant paper is positioned an aluminum foil sheet 39also overlapping the sides of the cup 11. The two-layer film is securelyfastened to the cup by means of wire 41. Instead of wire 41, a circularspring may be used to securely clamp the film to the sides of the cup.To complete a moisture-impervious covering for cup 11, amoisture-resistant tape 42 is wrapped over wire 41 extending beyond theend of films 38 and 39.

The squibs 33 and 34 are actuated by an electrical impulse from thecockpit of the airplane, for example. The electrical impulse is passedinto the starter chamber, passes through contact point 16 into squibs 33and 34. When the cartridge case is unpainted and is made of electricalconducting material no special grounding means are needed. When thecartridge case is painted, as may be required for storage purposes, itis necessary to provide adequate grounding means for insuring properfiring of the squibs. In FIGURE 1, there is set out a particularlyeffective means for providing an electrical ground and also a safetydevice in the handling of the cartridge case prior to insertion in thechamber. This device is called a short-out clip and it comprises acurved portion 46 which extends over and is in spaced relation tocontact point 18. The curved portion is then joined to the exterior ofthe bushing in a manner to form a good electrical contact. In thisembodiment, a metal washer 47 provided with anti-vibration looseningteeth forms the contact between the curved portion 46 and the exteriorbushing 12. In storage and handling, the tip 48 of the short-out clipprevents accidental electrical contact with the contact point 18. Whenthe cartridge has been introduced into the starter chamber, curvedportion 46 is straightened somewhat, and tip 48 is set out in such aposition that when the chamber is closed, tip 48 is firmly touching thechamber and thereby provides a good electrical ground. Other means ofgrounding may readily be devised.

In the particular embodiment shown in FIGURE 1 the cup contains about 40grams of CCC grade blasting powder. The blasting powder grains aredepicted as ovals in the partial section, FIGURE 1. About 25 grams ofammonium nitrate propellant was cut into slabs and utilized as the lumpportion of the igniter mixture. These lumps are shown as the rectanglesin FIGURE 1.

In FIGURE 3, a thin-walled tubular body portion 61 is provided with ashallow groove 62. The tubular body portion may also be described as acylinder. The wall of body portion 61 is made thick enough to withstandthe handling requirements of turbojet starter cartridges. It is obviousthat the thickness of the wall will be dependent upon the type ofmaterial used. It has been found that with ordinary mild steel materialof construction sheet of 16 or 20 gauge is of sufficient strength.Groove 62 is positioned at about the midpoint of body portion 61 andruns around the entire periphery of the body portion. The depth of thegroove 62 is such that the means for sealing the slide joint of thestarter chamber will fit into the groove so as to provide asubstantially flush surface with respect to the exterior side of thetubular body portion wall. It is to be understood that the sealing meansneed not be exactly flush with the outside wall as the cartridge case isnot a sliding fit into the starter chamber.

Positioned in groove 62 are a plurality of apertures 63, 64, etc. Theseapertures are substantially uniformly spaced about the periphery of bodyportion 61. The function of apertures 63, etc. is to permit gas producedfrom the combustion of the solid propellant grain 66 to pass through thewall of the case and exert pressure on the sealing means. Apertures 63,etc. may be small holes, for example one-eighth inch in diameter or theymay be slots. The apertures 63, etc. are relatively small with respectto the width of groove 62. The apertures 63, etc. are substantiallyuniformly spaced around the periphery of the body portion 61 in order toinsure sealing of the entire joint surrounding the case, the joint inthe starter cartridge being located immediately adjacent the groove 62provided in body portion 61. It has been found that a plurality ofapertures are necessary in order to provide good sealing, the exactnumber of apertures being a function of the aperture size. Too large anumber of apertures or too large a size relative to the width of groove62 may cause destruction of the sealing means and permit leakage ofgases out of the chamber by way of the joint. The exact number ofapertures 63 and the size thereof may be readily determined by a smallnumber of tests for each type of seallng means.

The cartridge must not be damaged by the entrance of moisture into theinterior of the case. Moisture interferes with the proper burning of thesolid propellant. The apertures 63, etc. are covered with amoisture-impervious film 67 which extends around the periphery of thebody portion in groove 62. The moisture-impervious film 67 need not beimpervious in the precise sense of that word. Hereinaftermoisture-impervious is to be understood as a material which will preventwater entering the film of the particular thickness being used for atime substantially in excess of the specification requirement of nomoisture peneration after 2 hours exposure to a driving rain.

The means for sealing the joint of the chamber in an elastic ribbon-likemember 68 positioned in groove 62 and extending over apertures 63, etc.provided in the groove of body portion 11. Member 68, which may bedescribed as a rubber-like elastic band, extends over apertures 63, etc.an appreciable distance. Gases from the combustion of solid propellantgrain 66 break through the film 67 at apertures 63, etc. and exertpressure against band 68, expanding it against the joint in the starterchamber. It is preferred that band 68 be about the width and depth ofgroove 62. Band 68 may be any material which is sufiioiently elastic tobe expanded the distance between the outside wall of groove 62 and thesurface of the starter chamber to seal the joint in the chamber. Theelastic member or band 68 may be made of various synthetic materials,such as polyethylene or polyvinyl acetate which has been plasticized torender it elastic. It is preferred that band 68 be rubber-like incharacteristics and made from natural or synthetic rubbers. Because ofits resistance to temperature, silicone rubber is preferred as amaterial of construction for rubber-like member 68.

There is attached to one end of body portion 61 a thinwalled end-closuremeans 71. End-closure means 71 may be fabricated integrally with bodyportion 61 or may be attached thereto by welding or by nuts and bolts orby rivets. It is desired that end-closure member 71 be substantiallyrigidly attached to body portion 61. It has been found that mild steelsheet of 16 gauge thickness is more than adequate for use in end-closuremeans 71.

End-closure 71 is adapted for the mounting of igniter assembly hereindesignated as numeral 73. Usually endclosure 71 will be provided with ahole which is centrally located with respect to the long axis of bodyportion 61 into which the igniter assembly is mounted by meanshereinafter described.

End-closure means 71 is provided with a plurality of apertures 76, 77,etc. These apertures 76, etc. are positioned on the end-closure so as topermit free flow of gases from the interior of the case through theapertures. The presence of combustion gas on the exterior of theend-closure end of the case has some beneficial effect on the operationof the starter, the number of apertures 76, etc. to be determined by thesize of the aperture and also by the solid propellant itself. Ingeneral, 3 or 4 one-eigth inch apertures appears to be suflicient. Theseapertures 76, etc. should be placed uniformly on the end-closure aboutthe central point thereof.

To exclude moisture from the interior of the case, apertures 76, etc.are covered by moisture-impervious film means. Apertures 77 in FIGURE 4is shown covered by moisture-impervious film means 81. The film meansused to cover apertures 76, etc. may be of the same material ofconstruction as the films means 67 used to cover apertures 63, etc.

Solid propellant grain 66 is, in this embodiment, a tube. A gas flowpassage must be provided along the interior wall of tubular portion 61.The outside diameter of grain 66 is set relative to the internaldiameter of body portion 61 so that the necessary predetermined spacingfor the flow of gases at the initial combustion is set. Grain 66 iscushioned against handling by means of resilient members positioned bothon the cylindrical sides of the grain and also on the flat bottom andtop sides. In this embodiment, four resilient side members and endmembers are utilized at each end of the grain to provide this support.In FIGURE 3, upper resilient side member 86 and lower resilient sidemember 87 are shown, the number of resilient members to be determined inpart by the type of solid propellant used and also the material ofconstruction of the resilient members themselves. The resilient membersmay be made from spring-like materials and may even be coil springs.However, it is preferred that the resilient members be made of materialssuch as felt, rubber, or cork. Felt is a particularly good material. Theresilient side members are adapted to maintain a predetermined spacingbetween the interior side of the body portion wall and the exterior ofthe grain 66; or this may be described as a predetermined spacingbetween the interior of the body portion 61 and the inner surface of theside member since the inner surface of the side member must be incontact with the outer surface of the grain. The upper resilient sidemembers are supported near the end-closure means.

Upper resilient end-members 87, etc., are supported near end-closuremeans 71 and are adapted to maintain a predetermined spacing between theinner side of the end-closure wall and the inner surface of the upperend member, i.e., the upper end of grain 66. In this embodiment, theupper side member and upper end member 86 and 87 respectively are formedout of one L-shaped piece of resilient material and are mounted againstthe inner wall of tubular portion 61. The upper members are supported bymeans of an apertured doughnut plate 89 which is spaced from theend-closure by means of legs 91, 92, 93 (and 94 not shown). These legsare spot-Welded to the inner surface of end-closure 71. Also, the flatportion of plate 89 is spot-Welded to the inner wall of body portion 61.Holes 96, etc. are provided in plate 89 to permit free flow of gasesfrom igniter 73 along the inner wall of body portion 61 and therebycontacting of the exterior surface of grain 66. It is self-evident thatother methods of supporting the resilient members may be devised, forexample, individual metal portions just large enough to hold theresilient members. The side members may be readily attached to theinterior of the body portion by adhesive when it is desired to useseparate end members and side members.

At the end of the body portion 61 opposite that containing end-closure71, there is a thin walled screen-like member 101. This screen-likemember 101 is adapted to be attached to the end of the body portion 61opposite that wherein end-closure 71 is attached. In this embodiment,the attachment is made by means of snap-on means positioned on the endof body portion 61 and on the flange 101 of member 101.

Screen-like member 101 is provided with a spacing element 111. Spacingelement 111 provides a spring action which works against the bottom ofthe starter chamber to force the igniter assembly electrical contactpoint against the electrical connection positioned in the upper end ofthe chamber. Screen-like member 101 is provided with a multiplicity ofholes which extend through the wall of the member. These holes occupysubstantially all of the portion of the member except for that taken upby the spacing element 111. The holes permit the substantiallyunobstructed flow of combustion gases from propellant 66 out of thecartridge case and on into conduit leading to the starter turbine. Inthis regard, spacing element 111 also provides the necessary clearingbetween the bottom of the starter chamber and the case to form a passagepermitting the flow of the combustion gases. The holes in screen member101 are of a size such that any unburned lumps of propel-lant will beretained in the case until reduced to size which will not clog theconduit leading to the starter turbine. Screen member 101 is formed ofmaterial of sufl'icient thickness to impart the necessary strength tothe member in view of the multiplicity of holes therein.

Resilient members are provided at the screen member end of the bodyportion to maintain the predetermined spacing between the inside Wall ofthe body portion 61 and the cylindrical side of the grain 66. Also, theresilient members maintain a predetermined spacing between the screenmember and the end of the grain 66. In FIGURE 3, lower resilient sidemember 121 and lower resilient end member 122 are shown. Actually inthis embodiment four lower resilient side members and four lowerresilient end members, in the form of an L-shaped piece of felt, areutilized. The lower resilient members may be made of the same type ofmaterial and be of the same construction as the upper resilient members.In this embodiment, the L-shaped lower resilient end members are notfastened to the wall of tubular body portion 61. The clearance betweenthe screen member 101 and the end of grain 66 is such that the resilientmembers are held in place by pressure from the screen member 101 when itis locked onto the end of body portion 61. However, suitable means forfixedly attaching the lower resilient members may be readily devised.

In order to exclude moisture from entering the case by way of screenmember 101, a moisture-impervious film 124 is placed over the open endof body portion 61 after the lower resilient members have been put intoplace. The film 124 extends not only over the open end but overhangs thesides of portion 61 and is crimped between the flange 102 of screenmember 101 and the end of the body port-ion 61. Moisture-impervious film124 is preferably made of a plastic or rubberized material which, whileexcluding moisture, will disintegrate substantially instantaneously whenpressure is imposed on it by the combustion gases from the burning ofgrain 66. Film 124 may be made of a very thin metal such as aluminumfoil, although it is preferred that a combustible film be used.Polyethylene film is particularly suitable.

The igniter assembly used in a full size gas generator cartridge isdescribed in detail. Igniter cup 11 used in this particular embodimentwas 2% inches in outside diameter provided with a turned-over edgespaced somewhat from the cup so that the total overall diameter was 2%inches. The curved portion of the cup was a section of a sphere having aradius of inches. The bushing which extends through a centrally locatedhole in the cup was machined to provide a threaded portion on theexterior of the bushing and a necked-in straight portion. The totallength of the bushing was $4 inch with the threaded portion beingone-half the length. The interior of the bushing was machined to providea shoulder on which to rest a washer. Electrical conductor rod 17 madeof A inch drill rod and about inch overall length was passed through theinterior of bushing 12. A brass washer was silver soldered to the end ofrod 17 to provide a contact point. The contact point was Vs inch indiameter. A silicone rubber insulator in the form of a cup extends belowthe brass washer of the contact point and up the sides, insulating therod and the washer from the bushing. Beneath the silicone rubber waspositioned a hard fiber washer which rested on the shoulder insidebushing 12. A silicone rubber tube was placed around rod 17 and passedup into the bushing to insulate the rod from the bushing. A copperwasher was placed around the inside end of the bushing inside the cupand the end of the bushing was then crimped against the washer to firmlyseat the washer and the bushing against the curved end of cup 11. Afemale solderless terminal, capable of holding two No. 22 gauge copperwires, was attached to washer 14. A hard fiber washer was passed up rod17 and was held rigidly against the cn'mped end of bushing 12 by meansof a one-piece nut. A female terminal was then attached to the interiorend of rod 17. Two regular electrical squibs were then attached to theterminals as shown in FIGURE 2.

The igniter cup was then filled with ignition mixture. The ignitionmixture was held in place by means of a sisalkraft paper and aluminumfoil sheet, the ends of which were securely wired to the cup below theflange 36. Drafting tape was then used to moisture-proof the edge ofthis paper-foil seal.

Thus having described the invention, what is claimed 1. An igniterassembly comprising a vessel, having an open end, an igniter mixture,positioned in said vessel, consisting essentially of (a) a number ofgrains of a powder member selected from the class consisting of blackpowder, magnesium powder-potassium nitrate mixture, aluminumpowder-potassium nitrate mixture, aluminum powder-alkali metalperchlorate mixture and magnesium powder-alkali metal perchloratemixture and (b) a number of lumps consisting essentially of ammoniumnitrate, an oxidizible binder and a combustion catalyst, the ammoniumnitrate being the predominant component, said lumps having a minimumdimension of at least about Vs inch and a maximum dimension of not morethan about inch, said igniter mixture containing an amount of saidpowder member at least sufiicient to initiate sustained combustion ofsaid lumps, readily destructible means for maintaining said mixturewithin said vessel and means, positioned within said vessel, adapted forinitiating burning of said powder member.

2. The assembly of claim 1 wherein said lumps are approximately cubicalin shape of about inch on a side.

3. The assembly of claim 1 wherein said powder member is black powderhaving an average screen size between about /1 and /1 inch.

4. An igniter assembly comprising a cup-like member, an igniter mixturepositioned in said cup consisting essentially of (a) black powder grainshaving an average screen size between about 1 1 and inch and (b) anumber of lumps consisting essentially of ammonium nitrate, anoxidizable binder and a combustion catalyst, said lumps containing atleast about weight percent of ammonium nitrate, said lumps having aminimum dimension of at least about /a inch and a maximum dimension ofnot more than about inch, said igniter mixture containing between about3 parts by weight of powder per part of lumps present and about 1 partby weight of powder per part of lumps present, readily destructiblemeans for maintaining said mixture within said cup and means, positionedin said cup, adapted for initiating burning of said black powder.

References Cited in the file of this patent UNITED STATES PATENTS802,347 Aspinwall Oct. 17, 1905 2,124,201 Lewis July 19, 1938 2,398,683Whitworth Apr. 16, 1946 2,434,872 Taylor Jan. 20, 1948 2,530,493 VanLoenen Nov. 21, 1950 2,561,670 Miller July 24, 1951 2,637,274 Taylor May5, 1953 2,696,191 Sheehan Dec. 7, 1954 FOREIGN PATENTS 10,883Netherlands July 15, 1924 655,585 Great Britain July 25, 1951

1. AN IGNITER ASSEMBLY COMPRISING A VESSEL, HAVING AN OPEN END, ANIGNITER MIXTURE, POSITIONED IN SAID VESSEL, CONSISTING ESSENTIALLY OF(A) A NUMBER OF GRAINS OF A POWDER MEMBER SELECTED FROM THE CLASSCONSISTING OF BLACK POWDER, MAGNESIUM POWDER-POTASSIUM NITRATE MIXTURE,ALUMINUM POWDER-POTASSIUM NITRATE MIXTURE, ALUMINUM POWDER-ALKALI METALPERCHLORATE MIXTURE AND MAGNESIUM POWDER-ALKALI METAL PERCHLORATEMIXTURE AND (B) A NUMBER OF LUMPS CONSISTING ESSENTIALLY OF AMMONIUMNITRATE, AN OXIDIZIBLE BINDER AND A COMBUSTION CATALYST, THE AMMONIUMNITRATE BEING THE PREDOMINANT COMPONENT, SAID LUMPS HAVING A MINIMUMDIMENSION OF AT LEAST ABOUT 1/8 INCH AND A MAXIMUM DIMENSION OF NOT MORETHAN ABOUT 5/8 INCH, SAID IGNITER MIXTURE CONTAINING AN AMOUNT OF SAIDPOWDER MEMBER AT LEAST SUFFICIENT TO INITIATE SUSTAINED COMBUSTION OFSAID LUMPS, READILY DESTRUCTIBLE MEANS FOR MAINTAINING SAID MIXTUREWITHIN SAID VESSEL AND MEANS, POSITIONED WITHIN SAID VESSEL, ADAPTED FORINITIATING BURNING OF SAID POWDER MEMBER.